1. Field of Invention
The processes and apparatuses of the present invention are to be used in absorption refrigeration systems, each using a volatile solvent such as water and a non-volatile solute such as lithium bromide, lithium chloride and calcium chloride, that are used to attain high level refrigeration.
A conventional absorption refrigeration system uses a single step vapor absorption using an aqueous lithium bromide solution. The degree of temperature lifting attainable is relatively small. A system of the present invention uses more than one step of vapor absorption and can attain a higher degree of temperature lifting.
A system of the present invention is characterized in using low grade heat, such as waste heat, in accomplishing a high degree of temperature lifting of heat energy. A multi-effect absorption refrigeration system may be considered as a reversed system of a multiple effect evaporation system.
The processes and apparatuses may be used in the following systems:
(1) Systems for conducting solid-liquid-vapor(S/L/V) multiple phase transformation processes such as vacuum freezing processes, distillative freezing processes and vacuum freezing eutectic freezing processes.
(2) Systems for conducting two phase fractional crystallization processes such as in dewaxing of lubrication oil and column crystallization.
(3) Chemical processing systems such as in recovery of condensable components out of gas streams, e.g. recovery of condensable hydrocarbon from natural gas.
(4) Systems for conducting freeze drying.
(5) Systems for making ice and ice cream.
(6) Systems for cool storage (thermal storage).
(7) Systems for product cooling such as in meat packing.
(8) Systems for cooling liquids such as fruit juices, beer and wine.
2. Brief Description of Prior Art
A commercial absorption refrigeration unit has (a) an evaporator section, (b) an absorber section, (c) a generator section, and (d) a condenser section.
An absorption refrigeration unit uses water as the refrigerant under a deep vacuum. The unit operates on the simple principle that under low absolute pressure (vacuum), water takes up heat and vaporizes at a low temperature. For example: at 0.25 inches of mercury absolute pressure, water boils at 40 degrees Fahrenheit. To obtain the energy required, it takes heat from and there chills, another liquid (usually water). The chilled liquid can then be used for cooling purposes. These operations are conducted in the evaporator section of the unit.
To make the cooling process continuous, the vaporized refrigerant water is absorbed by an absorbing solution, usually a lithium bromide water solution. The removal of refrigerant vapor by absorption keeps pressure in the evaporator section low enough for vaporization to continue. Heat of absorption is released and is removed through heat transfer coils by a stream of cooling water. The absorbing solution becomes a diluted absorbing solution. These operations are conducted in the absorber section of the unit.
The diluted absorbing solution is pumped to the generator section where water is vaporized from it at a pressure considerably higher than that in the evaporator section described. A stream of high pressure vapor and concentrated absorbing solution are formed. These operations are conducted in the generator section of the unit. The concentrated absorbing solution is heat exchanged with the diluted absorbing solution and is then returned to the absorber section.
The high pressure water vapor is condensed by heat exchange with a stream of cooling water to form a condensate. The condensate is returned to the evaporator section.
The chilled water produced by a conventional single effect absorption refrigeration is generally limited to 40 degrees Fahrenheit. The temperature limit attanable by a single effect operation is set by the need of using cooling water near or above ambient temperature and by a limitation of formation of lithium bromide hydrate crystals and anhydrous lithium bromide crystals.